Recombinant DNA clones of the whole and partial genomes of two strains of Moloney MSV, as well as the MSV related normal cell sarc sequence of Balb/c mice, have been isolated and characterized biochemically. We are attempting to define the role of specific regions of the MSV genome in the transformation process by measuring the ability of portions of the MSV genome to transform normal mouse cells in a DNA transfection assay. We are also trying to determine the specific events required to enable normal cell src sequences to express a transforming function.